The VTF-3 MK4 is likely very similar to the Outlaw Audio LFM-1 EX in max SPL (the OA subs were designed by Dr. Hsu). Data-bass.com has measurements on the Outlaw EX and the FV15HP, and the Rythmik beats the the hell out of it.
I would expect better SQ, too, because of the direct servo driver.